In the airline industry, temperature-controlled cargo containers are utilized to ship temperature sensitive items, for example, blood, plasma and vaccines. The interior temperature of the cargo container is maintained using a refrigeration system. Refrigeration systems typically comprise a refrigeration compressor, a refrigeration condenser, and exhaust fans.
Exhaust fans may operate to remove heat from the interior of a refrigerated cargo container such as for example, by directing airflow over a condenser and exhausting the air to the external environment. Under normal operating conditions, the external direction of airflow is not an issue. However, when transported onboard an airplane, the flow of exhaust air and/or heat from the refrigerated cargo container may impair the ability of the airplane's smoke detection system to detect a smoke event and to alert the crew of an emergency. Further, in the event that an airplane's fire suppression system is activated, air currents generated by exhaust airflow from a refrigerated cargo container may impact the dispersal of the fire suppression agent, for example by changing the agent's concentration levels and therefore, its knockdown capabilities.
Since fires and the threat posed by them develop rapidly, the earliest possible warning of the outbreak of a fire is desired so that appropriate actions may be taken to mitigate damage. Thus it is vital to quickly detect the changes in the local environment of a fire. These changes may be referred to as fire signatures. Once produced by a fire, fire signatures must travel to a detector to produce a response, such as an alert.
The balance between early warning and minimum false alarms requires that sensors be selected to match their applications in terms of the characteristics of expected fires in the operating environment. An analysis of combustible materials and potential ignition sources aboard an airplane can provide insight into the expected fire signatures that will be produced.
Currently, cargo containers comprise smoke, relative humidity, temperature and/or particulate detectors which can reduce the speed of, or shutdown a container's exhaust fans when fire or smoke is detected. Yet an infinite combination of combustibles, flammable liquids and/or electrical equipment may be present in the cargo hold of an airplane on any given flight. It stands to reason that a fire in an airplane may produce fire signatures beyond those that are detectable by the aforementioned detectors at the initiation of a fire.
Thus, there is a need to have a shutdown system for use with a refrigerated cargo container that can quickly respond to a variety of fires and shutdown or restrict the container's exhaust airflow. There is also a need for a system that proactively shuts down or restricts the exhaust airflow when air transit is detected. Moreover, a shutdown system that minimizes false alarms is desired. Additionally, there is a need for a shutdown system that does not require a user to initiate the shutdown or restriction of the container's exhaust airflow.